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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-953) Enable merge join in pig to work with loaders and store functions which can internally index sorted data
Date Thu, 10 Sep 2009 21:57:57 GMT

    [ https://issues.apache.org/jira/browse/PIG-953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753843#action_12753843
] 

Alan Gates commented on PIG-953:
--------------------------------

-1 to adding an orderPreserving flag on operators.  We have no intention of ever promising
that any relational operator beyond Order and Limit preserve order.  The fact that some happen
to now (like filter) is a side effect of the current implementation, not a feature.  If we
add a flag, it becomes a feature that we will be expected to maintain.

> Enable merge join in pig to work with loaders and store functions which can internally
index sorted data 
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: PIG-953
>                 URL: https://issues.apache.org/jira/browse/PIG-953
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 0.3.0
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>         Attachments: PIG-953.patch
>
>
> Currently merge join implementation in pig includes construction of an index on sorted
data and use of that index to seek into the "right input" to efficiently perform the join
operation. Some loaders (notably the zebra loader) internally implement an index on sorted
data and can perform this seek efficiently using their index. So the use of the index needs
to be abstracted in such a way that when the loader supports indexing, pig uses it (indirectly
through the loader) and does not construct an index. 

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